diff --git a/js/common.js b/js/common.js
new file mode 100644
index 0000000..0d79504
--- /dev/null
+++ b/js/common.js
@@ -0,0 +1,45 @@
+// Theme management
+// Check for saved theme preference or default to light mode
+const currentTheme = localStorage.getItem('theme') || 'light';
+document.documentElement.setAttribute('data-theme', currentTheme);
+
+function toggleTheme() {
+    const theme = document.documentElement.getAttribute('data-theme');
+    const newTheme = theme === 'light' ? 'dark' : 'light';
+    
+    document.documentElement.setAttribute('data-theme', newTheme);
+    localStorage.setItem('theme', newTheme);
+    
+    // Update icon
+    const icon = document.querySelector('.theme-toggle-slider i');
+    icon.className = newTheme === 'light' ? 'fas fa-moon' : 'fas fa-sun';
+}
+
+// Set initial icon on page load
+window.addEventListener('DOMContentLoaded', (event) => {
+    const theme = document.documentElement.getAttribute('data-theme');
+    const icon = document.querySelector('.theme-toggle-slider i');
+    if (icon) icon.className = theme === 'light' ? 'fas fa-moon' : 'fas fa-sun';
+});
+
+// Menu dropdown toggle
+function toggleMenu() {
+    const dropdown = document.querySelector('.menu-dropdown');
+    const btn = document.querySelector('.menu-button');
+    const willShow = !dropdown.classList.contains('show');
+    dropdown.classList.toggle('show');
+    if (btn) btn.setAttribute('aria-expanded', willShow ? 'true' : 'false');
+}
+
+// Close dropdown when clicking outside
+document.addEventListener('click', function(event) {
+    const menuWrapper = document.querySelector('.menu-wrapper');
+    if (menuWrapper && !menuWrapper.contains(event.target)) {
+        const dropdown = document.querySelector('.menu-dropdown');
+        if (dropdown) {
+            dropdown.classList.remove('show');
+            const btn = document.querySelector('.menu-button');
+            if (btn) btn.setAttribute('aria-expanded', 'false');
+        }
+    }
+});